Semicrystalline plastics and amorphous elastomers when mixed are normally immiscible and form a dispersion, i.e. a mixture of the two results in a polymer blend with the tendency of separating into distinct phases of uniform intraphase composition and distinct interphase composition. Physical mixing methods are common for creating such dispersions. An example of a physical method is making a semicrystalline plastic (SP) and amorphous elastomer (AE) separately and mixing the two in the molten state in an intensive, mixer such as a Brabender mixer.
Efforts have been directed at creating an intimate dispersion of SP and AE. "Intimate dispersion" is defined as intermingling of SP and AE components to a level finer than would be expected from mixing the components via physical methods. Intimate mixing is a measure of the surface area of contact between the dissimilar polymers and is related to the inverse of the physical size of the particulate dispersion of the two components of the mixture. Evidence of an intimate dispersion can be determined by a morphological examination of the polymer dispersion and is also apparent in the evaluation of the mechanical, thermal and solubility properties of the mixture. It is well known that the degree of mixing of normally immiscible polyolefin polymers affects the properties of physical blends of polymers. Highly dispersed mixtures give benefits in impact strength, toughness, and the depression in the ductile to brittle transition temperature of the blends. These improvements in the mechanical properties of a blend of polymers on increasing the interfacial surface area of contact and the consequent decrease in the particle size of the dispersion has been described in the book "Polymeric Compatibilizers: Uses and Benefits in Polymers Blends" by Datta, et al., Section 1 published by Hanser Verlag (1996). Because of the many benefits of intimate mixtures, a variety of methods have been used to attain intimate mixing of immicible polyolefin polymers.
One method of making intimate mixtures of SP and AE is disclosed by Yamaguchi, et al. in the Journal of Applied Polymer Science Volume 62, pp. 87-97 (1996) who teach that blends of polypropylene and copolymers of ethylene with alpha olefins containing greater than 3 carbon atoms, specifically butene and hexene, form intimate mixtures in certain specific composition ranges of the alpha olefin. Such a procedure was restricted to certain specific compositions since polymer dispersions composed of ethylene and propylene did not form intimate mixtures and neither did other copolymers of ethylene beyond the specified composition range. A similar set of data has been shown by U.S. Pat. No. 4,966,944, U.S. Pat. No. 4,742,106, U.S. Pat. No. 4,774,292, and U.S. Pat. No. 5,391,618.
A second method of making intimate mixtures comprising SP and AE is the use of vinyl unsaturation in a polymer made in the first reactor as a method to incorporate chemical links between the polymer made in the first and the second reactors and thus obtain an intimate mixture of polymer. Datta, et al., in a publication in the journal Macromolecules v 24, pp. 561-566 (1991) have shown the sequential polymerization of amorphous elastomer followed by a SP component. The polymer dispersion incorporates a diene monomer, vinyl norbornene and 3-butenyl norbornene being exemplified, which leave a pendant vinyl unsaturation on the polymer backbone material being made in the first polymerization reactor. The amount of the vinyl unsaturation is measured by infra red spectroscopic techniques and is estimated to be equivalent to 6 to 10 vinyl groups per polymer chain. The product of this sequential polymerization is intimately mixed only when dienes containing residual vinyl unsaturation are used. Addition of any other type of diene or the generation of a functionality which is not vinyl unsaturation does not lead to the formation of an intimate mixture of polyolefins. The use of such dienes can lead to highly branched structures which are undesirable in many end use applications.
A third method of making intimate mixtures comprising SP and AE is described by Feng et al. in the journal Acta Polymerica Sinica vol. 2, p125 (1987) wherein the AE consists of a broad composition distribution (CD), multicomponent mixture. Detailed analysis of the copolymer shows a continuum of the compositions which cover a range from polypropylene to polyethylene. This feature has been discussed by Simonazzi in a paper in the journal Pure and Applied Chemistry v. 56, p 625 (1984). These intimate blends of SP and AE are different from the blends of the present invention in the broad compositional range of the AE. Also, they are not synthesized in a solution polymerization process.
A fourth method of making intimate mixtures comprising SP and AE is by addition of a polymeric compatibilizer. For example, Datta, et al., in Macromolecules v. 26, p2064 (1993), and Kontos in U.S. Pat. Nos. 3,853,969 and 3,378,606, disclose the formation of blends of isotactic polypropylene as an SP component and an AE composed of copolymers of propylene with ethylene and hexene. These polymer blends are intimate mixtures but their formation requires the use of a compatibilizer such as a branched polymer in the case of Datta, et al., or a linear multiblock polymer in the case of Kontos. The blends are not intimately mixed in the absence of the compatibilizer.
A fifth method of making intimate mixtures comprising SP and AE is disclosed by Lynch, et al., in ACS Division of Polymeric Materials: Science and Engineering--Preprints v. 71, 609 (1994) who carefully coprecipitate a solution of AE (an ethylene propylene copolymer) and a SP (polypropylene). However, such a method makes a product which is not thermodynamically stable in the degree of intimate mixing since on heating for a short period of time above the melting point of the polypropylene, the degree of mixing of the phases deteriorates to that corresponding to a simple mixture of preformed polypropylene and amorphous ethylene propylene copolymer.